linux-ext4 - Re: confused on different inode size

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Message-ID: <20070409152630.GA30658@thunk.org>
Date:	Mon, 9 Apr 2007 11:26:30 -0400
From:	Theodore Tso <tytso@....edu>
To:	coly <colyli@...il.com>
Cc:	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: confused on different inode size

On Mon, Apr 09, 2007 at 10:33:13AM +0800, coly wrote:
> Theodore:
> 
> Thanks for your replying. 
> 
> Can I understand this way:
> * Though sizeof(struct ext4_inode) is 152, the real inode size on disk
> still depends on mount options.

Not mount options, but how the filesystem is formatted.  So substitute
"mount" with "mke2fs", and that would be correct.

> * If use old inode size, the on disk inode will be 128 bytes.
> * If use new inode size(e.g. extent option in mount), the on disk inode
> will be 256, or more bytes.

s/mount/mke2fs/

And the on-disk inode size is 256, 512, or some greater power of two,
up to the filesystem blocksize.

> * If on disk inode size is 128 bytes, only first 128 bytes of struct
> ext4_inode take effects.

Well, there's no space to store the fields beyond the first 128, so
any features that require the extra inode fields can't be used.

						- Ted
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